TY - JOUR

T1 - Microstructure by design

T2 - An approach of grain refinement and isotropy improvement in multi-layer wire-based laser metal deposition

AU - Froend, Martin

AU - Ventzke, Volker

AU - Dorn, Falk

AU - Kashaev, N.

AU - Klusemann, Benjamin

AU - Enz, Josephin

N1 - Funding Information: The authors would like to thank Mr. R. Dinse and Mr. P. Haack from Helmholtz-Zentrum Geesthacht for their valuable technical support. B. Klusemann acknowledges support from the Helmholtz-Association via an ERC-Recognition-Award under contract number ERC-RA-0022. Publisher Copyright: © 2019 The Authors

PY - 2020/1/20

Y1 - 2020/1/20

N2 - The additive production of metallic components with high-throughput is usually associated with high process temperatures and slow cooling rates. This typically results in strongly oriented columnar grain growth along the building direction of the structure having exceedingly large grain sizes. As a result, such structures show typically low strength and anisotropic mechanical behaviour in as-deposited condition. Consequently, post-processing is commonly performed to homogenize and eventually increase the mechanical properties of the deposited structures. In this regard, precise control of the applied process energy allows a modification of the local temperature distribution and cooling conditions during the additive manufacturing process, which strongly influence the resulting solidification microstructure. The aim of the present study is the development of an approach that allows to influence the solidification conditions in wire-based laser metal deposition of an Al-Mg alloy through specific adjustments of the laser irradiation. It was found that significantly different solidification microstructures in as-deposited condition can be achieved by adjusting the laser beam irradiance within a range resulting in conduction mode welding conditions while keeping the heat input constant. The application of high laser beam irradiances, close to the transition to keyhole mode welding, results in structures with a homogeneous large-grained solidification microstructure exhibiting a degree of anisotropy of around 12% between building direction and the direction of deposition. In contrast, the use of low laser beam irradiance close to the lower limit of stable melting, results in structures with a significantly refined microstructure. Consequently, an increase of yield strength of up to around 20% and microhardness of up to 13%, as compared to structures processed with high laser beam irradiance, could be obtained. Moreover, the anisotropy of the as-deposited structure was reduced to a degree lower than 2%.

AB - The additive production of metallic components with high-throughput is usually associated with high process temperatures and slow cooling rates. This typically results in strongly oriented columnar grain growth along the building direction of the structure having exceedingly large grain sizes. As a result, such structures show typically low strength and anisotropic mechanical behaviour in as-deposited condition. Consequently, post-processing is commonly performed to homogenize and eventually increase the mechanical properties of the deposited structures. In this regard, precise control of the applied process energy allows a modification of the local temperature distribution and cooling conditions during the additive manufacturing process, which strongly influence the resulting solidification microstructure. The aim of the present study is the development of an approach that allows to influence the solidification conditions in wire-based laser metal deposition of an Al-Mg alloy through specific adjustments of the laser irradiation. It was found that significantly different solidification microstructures in as-deposited condition can be achieved by adjusting the laser beam irradiance within a range resulting in conduction mode welding conditions while keeping the heat input constant. The application of high laser beam irradiances, close to the transition to keyhole mode welding, results in structures with a homogeneous large-grained solidification microstructure exhibiting a degree of anisotropy of around 12% between building direction and the direction of deposition. In contrast, the use of low laser beam irradiance close to the lower limit of stable melting, results in structures with a significantly refined microstructure. Consequently, an increase of yield strength of up to around 20% and microhardness of up to 13%, as compared to structures processed with high laser beam irradiance, could be obtained. Moreover, the anisotropy of the as-deposited structure was reduced to a degree lower than 2%.

KW - Additive manufacturing

KW - Aluminium alloy

KW - Direct energy deposition

KW - Grain refinement

KW - Laser irradiance

KW - Laser metal deposition

KW - Engineering

UR - http://www.scopus.com/inward/record.url?scp=85075896714&partnerID=8YFLogxK

U2 - 10.1016/j.msea.2019.138635

DO - 10.1016/j.msea.2019.138635

M3 - Journal articles

AN - SCOPUS:85075896714

VL - 772

JO - Materials Science and Engineering A

JF - Materials Science and Engineering A

SN - 0921-5093

M1 - 138635

ER -